Which style will horizontally center the inner <div> within the outer <div>?

<div id="outer">
  <div id="inner">Center Me!</div>
</div>

• [ ]

#inner {
  width: 50%;
}

#outer {
  width: 100%;
}

• [ ]

#inner {
  left: 0;
  right: 0;
  position: center;
}

• [ ]

#inner {
  text-align: center;
}

• [x]

#inner {
  width: 50%;
  margin: 0 auto;
}

Correct Answer:

• [x]

#inner {
  width: 50%;
  margin: 0 auto;
}